The optical waveguide is intended to mean a transmission path prepared by using a substance having an optical characteristic (hereinafter, referred to as an optical material) which uses light as an object to be transmitted.
The optical waveguide has a structure in which a cladding having a lower refractive index than that of a core is optically joined to an outside of the core extending in a propagation direction of the light, and the core mainly serves as an optical path.
The optical waveguide includes various structures such as a coaxial structure including a so-called optical fiber, and a plate-shaped structure.
The optical waveguide does not only propagate the light, but also, there is the optical waveguide in which an electric element required for transmission and a structure for branching an optical path or binding the optical paths are embedded.
Herein, when the term “structure” is used herein and in the following descriptions, this is used as a concept including a material to be used and a characteristic thereof in addition to a mechanical structure such as dimension of the optical waveguide.
As a simple example of the conventional optical waveguide, the optical waveguide having a sheet-like shape or a plate shape (hereinafter, referred to as a planar waveguide) is known (Non-Patent Literature 1).